Oh dear, 10 days missing.
My theories are:
She may have had a medical episode somewhere while taking a shortcut or checking out a new running route in a rural area and may be in a field/bushes somewhere.
She may have been involved in a hit & run and has been moved/taken somewhere rural.
We haven't heard about any husband/partner, ex or otherwise, but I don't suspect them as I think they would have been mentioned by now.
Hereford is a very safe, small town so I don't suspect murder or serious foul play in the middle of the day, if at all.
MOO.
It only takes one person to cause foul play in the middle of the day,however safe an area has previously been.
Julia James and Lindsay Birbeck are both cases of women murdered when walking alone during the day.